As a sealing device for preventing leakage of fluid from between relative sliding parts that perform relative reciprocating motion, relative rotational motion, or relative rotational reciprocating motion like a seal or the like for rotation of an AT, a CVT, etc. for an automobile, for example, a seal ring 100 depicted in FIG. 7, the seal ring 100 formed of an annular body made of resin, has mainly been used (Patent Document 1).
Such a seal ring 100 is, as depicted in FIG. 7(a), placed in an annular groove 200 formed in the outer periphery of one sliding part (a shaft) of the relative sliding parts and is used in such a way that the outer periphery thereof is brought into intimate contact with the other sliding part (a housing) 201. When fluid pressure P is exerted, the seal ring 100 is pressed against a side wall surface 202 on the lower-pressure side (the right side in the drawing) in the annular groove 200, is brought into intimate contact with two faces: a contact portion S1 that is a sliding surface between the seal ring 100 and the other sliding part 201 and a contact portion S2 at which contact with the side wall surface 202 of the annular groove 200 is made, and fulfills a sealing function.
Such a seal ring 100 is made of a resin material and, in consideration of the workability of placement into the annular groove 200, as depicted in FIG. 8, has a cut portion 101 with a structure in which a ring shape is completely cut in one place on the circumference of a circle of the seal ring 100.
When such an existing seal ring 100 is used for a long period of time in a high-temperature environment, a phenomenon occurs in which the seal ring 100 thermally expands in the annular groove 200 in the direction of the perimeter and end faces 101a and 101b of the cut portion 101 strike each other and cause creep, whereby the perimeter of the seal ring 100 is shortened when the temperature becomes a low temperature again.
When the perimeter of the seal ring 100 is shortened, as a result of the seal ring 100 being reduced in diameter, as depicted in FIG. 7(b), a gap 203 is formed between the seal ring 100 and the other sliding part 201 and, under load of fluid pressure P in a low temperature environment, a leak path occurs in which the fluid passes through the gap 203.
To address such a problem, as depicted in FIG. 9, a sealing device that uses a combined seal obtained by combining the seal ring 100 with a rubber-like elastic body 102, places the rubber-like elastic body 102 on the side where a groove bottom 204 of the annular groove 200 is located, and is placed in such a way that the rubber-like elastic body 102 forms a predetermined squeeze margin may be used (Patent Document 2).
According to such a sealing device, since intimate contact is always made in three faces: the contact portion S1 between the seal ring 100 and the other sliding part 201, the contact portion S2 between the seal ring 100 and the side wall surface 202 of the annular groove 200, and a contact portion S3 between the rubber-like elastic body 102 and the groove bottom 204 of the annular groove 200, even when the perimeter of the seal ring 100 is shortened by creep, the elastic force of the rubber-like elastic body 102 always brings the seal ring 100 into intimate contact with the side where the other sliding part 201 is located. This prevents the formation of a gap that creates a leak path of fluid.